In the semi-automatic welding and repair welding of articles such as gas turbine engine alloy components and the like, it is a general practice to add filler material in the form of a metal wire, ribbon, etc., which is introduced into a molten weld puddle or pool by an appropriate apparatus. Of course, as used herein, the term "wire" is intended to include other equivalent material forms as well. Relative motion is provided between the surface of the workpiece and the molten pool of filler material to provide a complete welding or repairing operation.
The molten weld puddle or pool may be formed using a variety of different heat producing devices. For example, an electric arc generated between an electrode and a work surface of the workpiece, a plasma arc, a laser, or other such heat producing means may be used to provide this pool.
A variety of different devices have been developed which are capable of performing the foregoing operation. Of particular interest is the method and apparatus disclosed in U.S. Pat. No. 4,159,410, issued to Cooper and assigned to the assignee of the present application. U.S. Pat. No. 4,159,410 illustrates a method and apparatus for applying a filler material to a workpiece in which a filler material or wire is selectively introduced into a heating/molten pool area which is formed on the workpiece in a reciprocating manner; intermittently introducing the wire into the region and withdrawing the wire from the region at a specified feed rate. In this manner, melting of the end of the wire occurs intermittently, providing various stated benefits. Application of the filler material to the workpiece proceeds on a continuous basis in this manner, as described in U.S. Pat. No. 4,159,410, the subject matter of which is incorporated by reference as if fully set forth herein.
Although the method and apparatus disclosed in U.S. Pat. No. 4,159,410 significantly improves the quality of the weld or repair weld which is produced, it has been found that this method and apparatus is capable of still further improvement. For instance, in using the foregoing apparatus, as well as other previously available devices, undesirable melting of the workpiece, and sometimes premature melting of the end of the filler wire, has been found to occur. In an effort to remedy these situations, a variety of different approaches have been developed, none of which have satisfactorily eliminated these problems. For example, U.S. Pat. No. 3,581,053, issued to Manze, discloses a technique which synchronizes weld current applied to a heating torch with feeding of the filler wire in a manner which produces a maximum current when the wire is farthest from the workpiece, and a minimum current when the wire is in contact with the workpiece. In this manner, a globule is formed on the feed wire at its maximum excursion, which globule is then detached from the feed wire by surface tension upon contact with the workpiece. A similar technique is disclosed in U.S. Pat. No. 3,934,110, issued to Dennis.
U.S. Pat. No. 3,627,977, issued to Aldenhoff, discloses a technique which initiates operation of the welding apparatus as the filler material contacts the surface of the workpiece, primarily as a safety feature to protect the operator of the apparatus. However, operation of the welding apparatus is not discontinued until after the entire welding operation is completed, and no program is developed for selectively discontinuing the application of current to the welding device in response to reciprocation of the filler material.
Accordingly, it may be seen that workers in this art have developed a variety of different techniques to regulate melting of the filler wire as it is applied onto the surface of the workpiece. However, none of the techniques developed to date have provided a method which satisfactorily assures proper melting of the workpiece and the filler wire in conjunction with an apparatus which makes use of a reciprocating wire feed action to form the weld puddle or pool.